Synchronous rectifier

Abstract

A synchronous rectifier including a first rectifier current path. The first rectifier current path has a first and second switching arrangement, which are arranged in series. The first switching arrangement includes a first switch and the second switching arrangement includes a second switch. A first current sensor is arranged to measure a current through the first rectifier current path; and a controller is arranged to operate the first switch and the second switch based on the current measured by the first current sensor.

1 . A synchronous rectifier comprising:
 a first rectifier current path comprising: a first switching arrangement and a second switching arrangement arranged in series;   wherein the first switching arrangement comprises a first switch operable to selectively provide a first current path through the first switching arrangement;   wherein the second switching arrangement comprises a second switch operable to selectively provide a first current path through the second switching arrangement;   the synchronous rectifier further comprising:
 a first current sensor arranged to measure a current through the first rectifier current path; and 
 a controller arranged to operate the first switch and the second switch based on the current measured by the first current sensor. 
   
     
     
         2 . The synchronous rectifier as claimed in  claim 1 , wherein the controller is arranged to operate the first switch and the second switch to a non-conducting state if the current measured by the first current sensor is less than a first threshold. 
     
     
         3 . The synchronous rectifier as claimed in  claim 1 , wherein the first switching arrangement comprises a second current path arranged in parallel with the first current path and configured to allow current to flow through the second current path only in a first direction; and
 the second switching arrangement comprises a second current path arranged in parallel with the first current path, and configured to allow current to flow through the second current path only in a first direction.   
     
     
         4 . The synchronous rectifier as claimed in  claim 1 , comprising a second rectifier current path comprising a third switching arrangement;
 the third switching arrangement comprising a third switch operable to selectively provide a first current path through the third switching arrangement;   wherein the controller is arranged to operate the third switch based on the current measured by the first current sensor.   
     
     
         5 . The synchronous rectifier as claimed in  claim 4 , comprising a second current sensor arranged to measure a current through the second rectifier current path;
 wherein the controller is arranged to operate the first switch and the second switch based on the current measured by the second current sensor.   
     
     
         6 . The synchronous rectifier as claimed in  claim 5 , wherein the controller is arranged to operate the first switch and the second switch to a non-conducting state if the current measured by the second current sensor is greater than a third threshold. 
     
     
         7 . The synchronous rectifier as claimed in  claim 4 , wherein the controller is arranged to operate the first switch and the second switch to a conducting state when:
 i) the first current sensor detects a first current condition;   ii) the second current sensor detects a second current condition; and   iii) an input voltage applied to the first rectifier current path is determined to have a predetermined polarity.   
     
     
         8 . The synchronous rectifier as claimed in  claim 7 , wherein the controller comprises an AND gate which is arranged to receive a first signal indicative of the first condition from the first current sensor, a second signal indicative of the second condition from the second current sensor, and a third signal indicative of the input voltage polarity from an inverter controller, and wherein the AND gate is arranged to output a control signal for controlling the first switch and the second switch. 
     
     
         9 . A synchronous rectifier comprising:
 a first rectifier current path comprising a first switching arrangement; and   a second rectifier current path comprising a second switching arrangement;   the first switching arrangement comprising a first switch operable to selectively provide a first current path through the first switching arrangement;   the second switching arrangement comprising a second switch operable to selectively provide a first current path through the second switching arrangement;   the synchronous rectifier further comprising:
 a first current sensor arranged to measure a current through the first rectifier current path; and 
 a controller arranged to operate the first switch and the second switch based on the current measured by the first current sensor. 
   
     
     
         10 . A converter comprising:
 an input stage arranged to provide an input waveform; and   a synchronous rectifier as claimed in any  claim 1 , arranged to rectify the input waveform.   
     
     
         11 . The converter as claimed in  claim 10 , wherein the input stage is a switched input stage comprising at least a first input stage switch arranged to be driven by a first input switch drive signal; and
 wherein the controller is arranged to operate the first switch and the second switch based on the first input switch drive signal.   
     
     
         12 . The converter as claimed in  claim 11 , wherein the first input switch drive signal is provided to a one shot pulse generating circuit and wherein the one shot pulse generating circuit is arranged to start generating an output pulse when it receives a start of an input pulse from the first input switch drive signal and is arranged to stop generating an output pulse at the earlier of i) an end of the input pulse or ii) when an output pulse time limit is reached; and
 wherein the controller is arranged to operate the first switch and the second switch based on the output pulse from the one shot pulse generating circuit.   
     
     
         13 . The converter as claimed in  claim 12 , wherein the converter is a resonant converter, wherein the input stage comprises a resonant circuit having a resonant period; and
 wherein the output pulse time limit is equal to or less than half the resonant period.   
     
     
         14 . A converter comprising:
 an input stage arranged to provide an output waveform;   a synchronous rectifier arranged to rectify the output waveform; and   a controller;   the synchronous rectifier comprising a first rectifier current path comprising a first switching arrangement;   the first switching arrangement comprising a first switch operable to selectively provide a first current path through the first switching arrangement;   the input stage comprising a resonant circuit, having a resonant period, the input stage being arranged to receive an alternating input waveform;   wherein, the controller is arranged to operate the first switch in a non-conducting state if the alternating input waveform has a first polarity for longer than a maximum duration;   wherein the maximum duration is equal to or less than half the resonant period.   
     
     
         15 . A method of operating a synchronous rectifier, the synchronous rectifier comprising:
 a first rectifier current path comprising a first switching arrangement and a second switching arrangement arranged in series;   the first switching arrangement comprising a first switch operable to selectively provide a first current path through the first switching arrangement;   the second switching arrangement comprising a second switch operable to selectively provide a first current path through the second switching arrangement;   the method comprising:
 measuring a current through the first rectifier current path; and 
 operating the first switch and the second switch based on the current measured through the first rectifier current path.